The present invention relates to hypodermic syringes, and relates more particularly to a safety hypodermic syringe which permits the needle holder with the needle cannula to be pulled backwards to the inside of the barrel by the plunger after injection, and permits the plunger to be disconnected from the rubber stopper and then inserted into the front end of the barrel to deform the needle cannula inside the barrel.
The needle cannula of a hypodermic syringe must be damaged after its use, and then properly disposed of. Taiwan patent publication no. 210509 discloses a safety hypodermic syringe which permits the needle cannula to be pulled backwards to the inside of the barrel after its use. However, this structure of safety hypodermic syringe must be used with a specially designed needle cannula. Another drawback of this structure of safety hypodermic syringe is that the deformed needle cannula will still project out of the barrel if the needle cap is disconnected. Taiwan patent publication no. 212301 discloses another structure of safety hypodermic syringe. This structure of safety hypodermic syringe still cannot be used with regular commercially available needle cannula. Taiwan patent application no. 82218049 discloses still another structure of safety hypodermic syringe. This structure of safety hypodermic syringe is designed to adapt any of a variety of commercially available needle cannulas. However, because the needle holder has an opening which is not sealed after the needle cannula has been moved to the inside of the barrel, the needle cannula will still project out of the barrel.